1. Field of the Invention
The present invention relates to a method for the manufacture of gallium arsenide thin film solar cells and in particular to a method wherein a germanium layer is applied to the substrate before the gallium arsenide layers are applied.
2. Description of the Prior Art
Research to develop a solar cell having a high conversion efficieny, efficiencies of higher than 20%, that is inexpensive to manufacture, and that is stable has not led to any satisfactory result. One such result, a thin film solar cell of amorphous silicon, can be cost-favorably manufactured by a glow discharge method, but these cells are unstable and have a very low conversion efficiency, roughly 5%.
Another such result, a crystalline silicon solar cell can also be cost-favorably manufactured in band or film form by growing the crystals using a high growth rate, but these cells have a low conversion efficiency. However, a high conversion efficiency can be obtained for these cells if the crystalline silicon solar cells are produced in accord with conventional crystal growing methods, that is, using a low growth rate. This in turn renders the cells relatively expensive to manufacture and unsuitable for mass production.
Another important factor to consider when manufacturing crystalline solar cells is the selection of a suitable initial material. This material should be inexpensive, simple to work with and have the purity appropriate to achieve a high conversion efficiency.
While thin film solar cells of gallium arsenide have a higher theoretical conversion efficiency (24 to 28%) than the aforementioned silicon solar cells, the manufacture of gallium arsenide epitaxy layers with an adequate grain size, preferably in columnar structure, presents difficulties. Also, the selection of an inexpensive substrate material having lattice matching properties is a further problem.
It would therefor be an improvement in this art to manufacture a solar cell which is stable, has a high conversion efficiency, and is inexpensive.